The present invention relates to golf balls and more particularly, the invention is directed to improving the control of the spin rate of golf balls and to a method for varying the spin rate of golf balls.
The spin rate of golf balls is the end result of many variables, one of which is the distribution of the density or specific gravity within the ball. Spin rate is an important characteristic of golf balls for both skilled and recreational golfers. High spin rate allows the more skilled players, such as PGA professionals and low handicapped players, to maximize control of the golf ball. A high spin rate golf ball is advantageous for an approach shot to the green. The ability to produce and control back spin to stop the ball on the green and side spin to draw or fade the ball substantially improves a player""s control over the ball. Hence, the more skilled players generally prefer a golf ball that exhibits high spin rate, in part, off scoring irons (7-PW).
On the other hand, the recreational players who cannot intentionally control the spin of the ball generally do not prefer a high spin rate golf ball. For these players, slicing and hooking the ball are the more immediate obstacles. When a club head strikes a ball improperly, an unintentional side spin is often imparted to the ball, which sends the ball off its intended course. The side spin reduces a player""s control over the ball, as well as the direct-line distance the ball will travel. A golf ball that spins less tends not to drift off-line erratically if the shot is not hit squarely with the club face. A low spin ball will not cure the hook or slice, but will reduce the adverse effects of the side spin. Hence, recreational players typically prefer a golf ball that exhibits low spin rate.
Reallocating the density or specific gravity of the various layers of a golf ball provides an important means of controlling the spin rate. In some instances, the weight from the outer portions of the ball is redistributed toward the center to decrease the moment of inertia, thereby increasing the spin rate. For example, U.S. Pat. No. 4,625,964 discloses a golf ball with a reduced moment of inertia having a core with specific gravity of at least 1.50 and a diameter of less than 32 mm and an intermediate layer of lower specific gravity between the core and the cover. U.S. Pat. No. 5,104,126 discloses a ball with a dense inner core having a specific gravity of at least 1.25 encapsulated by a lower density syntactic foam composition. U.S. Pat. No. 5,048,838 discloses another golf ball with a dense inner core having a diameter in the range of 15-25 mm with a specific gravity of 1.2 to 4.0 and an outer layer with a specific gravity of 0.1 to 3.0 less than the specific gravity of the inner core. U.S. Pat. No. 5,482,285 discloses another golf ball with reduced moment of inertia by reducing the specific gravity of an outer core to 0.2 to 1.0.
In other instances, the weight from the inner portion of the ball is redistributed outward to increase the moment of inertia, thereby decreasing the spin rate. U.S. Pat. No. 6,120,393 discloses a golf ball with a hollow inner layer with one or more resilient outer layers, thereby giving the ball a soft core, and a hard cover. U.S. Pat. No. 6,142,887 discloses an increased moment of inertia golf ball comprising one or more layer layers made from metals, ceramic or composite materials, and a polymeric spherical substrate disposed inwardly from the layer layers.
These and other references disclose specific examples of high and low spin rate ball with ranges of specific gravity, ranges of diameter for the core, and ranges of thickness for the outer layers, for example. They, however, do not offer any universal guidelines to control the spin rate of golf balls. Hence, there remains a need in the art for an improved golf ball with controlled spin rates.
The present invention is directed to a golf ball with a controlled moment of inertia. The present invention is also directed to a golf ball with a controlled spin rate. The present invention is further directed to a golf ball with a controlled spin rate, soft compression and high resiliency.
These and other embodiments of the invention are realized by a golf ball with its weight distributed among the layers within the core of the golf ball relative to a centroid radius to precisely control the moment of inertia of the ball. In accordance to one aspect of the present invention, the innermost core of the ball comprises a specific gravity reduced material, surrounded by a thin dense layer located either to the inside or to the outside of a centroid radius to create a high spin ball or a low spin ball, respectively, with high compression and a soft feel. The ball may also have additional specific gravity reduced layers or a wound layer to improve the play characteristics of the ball. According to another aspect of the invention, the inner core, the intermediate layer and the outer core may comprise a specific gravity gradient increasing toward the outside of the ball, or a specific gravity gradient increasing toward the center of the ball.